The Java EE 7 Tutorial
The JavaServer Faces lifecycle spans all of the execute and render processes of an application. It is also possible to process and render only parts of an application, such as a single component. For example, the JavaServer Faces Ajax framework can generate requests containing information on which particular component may be processed and which particular component may be rendered back to the client.
Once such a partial request enters the JavaServer Faces lifecycle, the information is identified and processed by a
javax.faces.context.PartialViewContext object. The JavaServer Faces lifecycle is still aware of such Ajax requests and modifies the component tree accordingly.
render attributes of the
f:ajax tag are used to identify which components may be executed and rendered. For more information on these attributes, see Chapter 13, "Using Ajax with JavaServer Faces Technology".